1. Field of the Invention
The present invention relates to a light receiving sensor suitable for use in a so-called active type of distance measuring device and, more particularly, to a light receiving sensor suitable for distance measurement which has a plurality of distance measuring areas.
2. Description of the Related Art
New types of light receiving sensors have recently been known in the field of distance measuring sensors. One type of light receiving sensor is arranged to measure one area through a plurality of light receiving areas (refer to FIG. 11). Another type of light receiving sensor is arranged in such a manner that distance measurement using a plurality of light receiving areas can be performed for the purpose of distance measurement which is adapted to a wide field of view so that a plurality of areas in the field of view can be measured (refer to FIG. 12).
Referring to FIG. 11, parts L1 to L3 represent light receiving sensor elements on which light reflected from a subject located on a closest-distance side is made incident. Parts L4 to L6 represent light receiving sensor elements on which light reflected from a subject located on a far-distance side is made incident.
Referring to FIG. 12, parts L12 and L10 represent light receiving sensor elements which correspond to the left portion of the field of view, parts L7, L8 and L9 represent light receiving sensor elements which correspond to the central portion of the field of view, and parts L11 and L13 represent light receiving sensor elements which correspond to the right portion of the field of view. The left portion (as viewed in FIG. 12) of each of the light receiving sensor elements L7 to L13 serves as an area on which light reflected from a subject located on the closest-distance side is made incident as described above, while the right portion serves as an area on which light reflected from a subject located on the far-distance side is made incident as described above.
To prevent saturation of an electrical circuit due to external light incident upon a, it is customary to minimize such a light receiving sensor. Particularly in a distance measuring device which is arranged to emit light toward a subject by means of light emitting means, receive light reflected from the subject and measure the distance to the subject, it is common practice to select a sensor configuration corresponding to the size of the light emitting part of an infrared light emitting diode (IRED) which constitutes the light emitting means.
To intensify light emitted from the IRED which constitutes the light emitting means, it is customary to insert a lens in front of the IRED or to mount a hemispherical dome (refer to FIG. 9) on an IRED package.
However, the conventional light receiving sensor has a number of problems because of its size. For example, in the case shown in FIG. 11, to perform positioning of the light receiving sensor with respect to an IRED image emitted by the IRED which constitutes the light emitting means, each element is adjusted so that the IRED image can be positioned in the area of a light receiving sensor element L4 corresponding to an intermediate distance. However, the IRED image is not necessarily positioned on another light receiving sensor element in a state similar to the state where the IRED image is placed when the positioning of the light receiving sensor is effected on the basis of the intermediate distance (positioning distance), due to various factors such as a positional deviation of a distance measuring optical system, an aberration of the distance measuring optical system, the degree of accuracy of chip mounting and a positional deviation of each light receiving sensor element. In particular, a light receiving sensor element which is located closer to or at the periphery of the light receiving sensor provides a sensor output which exhibits low linearity with respect to distance. As a result, there is the problem that adjustment is difficult, complicated or impossible.
Although the arrangement shown in FIG. 12 has a plurality of IREDs for distance measurement adapted to a wide field of view, if the diameter of an IRED dome is reduced for various reasons, right and left IRED images corresponding to off-axis positions are deformed by the aberrations of light emitting and receiving lenses as shown in FIG. 10. To improve a distance measuring capability, it is desired to minimize the portion of the IRED image that is formed offset from the corresponding light receiving sensor element. However, the presence of such an aberration makes it difficult to accurately cover the IRED image, thus leading to the lowering of the distance measuring capability. In addition, similarly to the arrangement of FIG. 11, the arrangement of FIG. 12 also involves the problems due to a positional deviation of each light receiving sensor element.